Inborn hypothyroidism

• the most common congenital endocrine disease (prevalence 1: 3000–4000);
• thyroid hormones play a key role in brain development, especially by 8 months of age (slightly less so by 3 years of age);
• without substitution treatment, irreversible brain damage occurs - at the clinical diagnosis, the brain is already irreversibly damaged;
• since 1985, nationwide neonatal screening has been introduced - determination of TSH levels;
• etiopathogenesis: in 75–80% thyroid dysgenesis (agenesis, aplasia, hypoplasia, hemithyroidism, cystic malformation, ectopy) or dyshormonogenesis (disorder of any stage of hormone synthesis or secretion; neonatal goiter), or rare isolated congenital central hypothyroidism (congenital TSH defect - cannot be detected by neonatal screening)
• clinical picture without treatment: initially only prolonged neonatal jaundice (due to transplacental transmission of thyroid hormones from the mother), later (in the first 2 - 3 months of life) failure, slower growth rate and bone maturation - late closure of the fontanelle, delayed eruption of deciduous teeth, muscle hypotension, omphalocele, constipation, hoarseness, thermoregulation disorders, anemia; even later growth failure, psychomotor retardation, sensorineural hearing loss
• neonatal goiter or thyroid gland of normal size
• 2-5 times increased risk of associated congenital malformations compared to other populations → ultrasound examination of the heart, kidneys and CNS is recommended
• laboratory findings: ↑ TSH, ↓ fT4; (for the central form ↓ TSH and fT4);
• therapy: lifelong levothyroxine replacement therapy (started as soon as possible); intestinal absorption of L-thyroxine is impaired by concomitant ingestion of fiber, soy milk, calcium or iron preparations and malabsorption.

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